Field of the Invention
The present invention relates to a technique of recognizing a pickable work from piled works, and picking it.
Description of the Related Art
There has been developed a three-dimensional measurement apparatus for recognizing a pickable work and performing three-dimensional measurement for the work in order to pick, using an industrial robot, works irregularly piled on a pallet. As the three-dimensional measurement apparatus, there is known an apparatus for measuring the three-dimensional positions and orientations of piled works by capturing the works by emitting pattern light. When performing three-dimensional measurement, a plurality of pickable candidate works may be found from the piled works. Even if, however, a plurality of candidate works are found, it is common practice to pick one of the works, and then perform irradiation with pattern light and image capturing again, thereby repeating three-dimensional measurement.
Japanese Patent No. 5201411 describes a technique in which if a plurality of candidate works are found, it is determined whether the positions of the candidate works have changed, and if there exists a candidate work whose position remains unchanged, three-dimensional measurement is not repeated, thereby shortening a tact time. Japanese Patent No. 5201411 describes a method of comparing two images captured before and after picking in order to determine whether the positions have changed. However, Japanese Patent No. 5201411 does not mention which of the plurality of candidate works is determined as a picking target work. Thus, when an attempt is made to obtain an image after picking in order to determine a position change, if the arm of a robot shields a candidate work, it becomes impossible to recognize a change in the position of the shielded candidate work, and it is impossible to determine whether the work can be selected as a next picking candidate. Therefore, in the method described in Japanese Patent No. 5201411, when obtaining an image after picking, if there is a candidate work shielded by the arm of the robot, it is necessary to wait until the robot arm retreats from a position above a pallet, thereby disabling shortening of a tact time.
Japanese Patent Laid-Open No. 2012-125886 describes a technique in which when a robot arm picks one of candidate works, a shield ratio as a ratio of an area where the remaining candidate works are shielded to the entire area is calculated, and a candidate work having a lower shield ratio is preferentially picked. In Japanese Patent Laid-Open No. 2012-125886, this technique makes it possible to obtain an image, after picking, of candidate works other than a picking target work without waiting until the robot arm retreats from a position above a pallet.
Japanese Patent Laid-Open No. 2012-125886 discloses a technique of picking candidate works from a candidate work which prevents the robot arm from shielding the remaining candidate works as much as possible. However, Japanese Patent Laid-Open No. 2012-125886 poses a problem that a tact time cannot be shorten so much since a shield ratio is calculated for each candidate work and thus the calculation load is heavy.